1. Field of the Invention
The invention relates to cellular communication apparatus and methods for supporting voice communications.
2. Discussion of the Related Art
Some wireless communication systems support spread spectrum communication formats such as code division multiplex access.
FIG. 1 shows a portion of a wireless cellular communication system 10 that supports spread spectrum communication formats. The shown portion of the wireless cellular communication system 10 includes cells 12, 13, 14, 15. The cells 12-15 provide coverage for wireless voice communications from and to a contiguous spatial region that preferably does not have large coverage holes.
Each cell 12-15 includes an associated wireless base station 20, 21, 22, 23. Each wireless base station 20-23 maintains a wireless link with wireless mobile devices 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 located in the associated cell 12-15. In particular, each wireless base station 20-23 generates a pilot beam that enables the wireless mobile devices 28-40 in the associated cell 12-15 to set up the wireless link with the wireless base station 20-23 of the same cell 12-15. Each wireless base station 20-23 provides a communication link between the wireless mobile devices 28-40 in the associated cell 20-23 and a standard communication network such as the public telephone network.
In the wireless communication system 10, very different numbers of wireless mobile devices 28-40 may be located in different ones of the cells 12-15. For that reason, the different cells 12-15 may support very different amounts of wireless communication traffic. In spread spectrum systems, the amount of communication traffic strongly correlates to the amount of interference experienced by the wireless mobile devices 28-40. For that reason, it has often been desirable to balance communication loads between neighboring cells. Since spatial distributions of the wireless mobile devices 28-40 often changed over short time periods, it was also preferable to perform such balancing of cell loads dynamically.
One method for dynamical balancing of cell loads is based on cell breathing. Cell breathing involves dynamically changing the sizes of the cells 12-15 of the cellular communication system 10. Such cell breathing is implemented by changing powers of pilot beams of the cells 12-15, i.e., to shrink or expand selected ones of the cells 12-15. By appropriately varying the powers of pilot beams in neighboring cells 12-15, cell boundaries can be displaced in a manner that reduces differences in wireless communication traffic between the various cells 12-15.
FIG. 2 illustrates the effect of a cell-breathing transformation on the portion of the wireless communication system 10 shown in FIG. 1. The cell-breathing transformation has shrunk the cell 13 in response to that cell 13 having a relatively heavier traffic load in the state of FIG. 1 and has expanded cell 14 in response to that cell 14 having a relatively lighter traffic load in the state of FIG. 1. The cell breathing has reduced the traffic load imbalance by moving cell-boundaries so that wireless mobile devices 34-35 were displaced from the cell 13 with the heavier initial traffic load to the neighboring cell 14 with the lighter initial traffic load.
While such cell-breathing transformations can aid to reduce load imbalances between the cells of the wireless communication system, cell breathing often produces coverage holes. In particular, a cell-breathing transformation usually involves reconfiguring wireless hardware devices such as transmitters of pilot beams. Due to geometric and/or physical constraints, such hardware reconfigurations often produce new spatial cells that incompletely cover the initial coverage region for the wireless communication system. For example, the cell-breathing transformation produced the state of FIG. 2, which includes two large coverage holes 42, 43. Due to geometric and/or physical constraints, none of the pilot beams of adjacent cell 12-15 serves the coverage holes 42, 43.
By generating such coverage holes, cell-breathing transformations can produce situations where some wireless mobile devices 30, 33 are not served by any of the neighboring cells. This deficiency of cell breathing is obviously undesirable in a cellular communication system.